Thanks! I appreciate the explanation. Presumably the reason for the retry is in case the device simply hasn't finished initialising the USB connection, or something like that?

That is one reason. Another is that the device might actually have been changed between scans.

I suppose we could detect that a given USB ID has failed N times in N tries and stop checking it until it disappears for a complete cycle (or something like that). My problem is that I have no motivation at all to take on this task, having neither a floppy drive nor a device that isn't fully recognized.